Environmental Protection Agency Administrator William D. Ruckelshaus went to the National Academy of Sciences yesterday to hear what the oracle of science had to say on acid rain.

The oracle was Delphic.

In an unusual session hosted by the academy at the EPA's suggestion, Ruckelshaus and White House science adviser George A. Keyworth heard four hours of spirited discussion among 15 leading scientists on the results of their research into acid rain.

The idea was to move forward on what Ruckelshaus calls the "risk assessment phase" of the Reagan administration's response to the problem of acid rain, which is blamed for killing aquatic life in hundreds of lakes and streams in Canada and the northeastern United States.

Once science has evaluated the risks involved in an environmental hazard, according to Ruckelshaus' theory, government decision makers can decide which risks are acceptable and how best to deal with the ones that aren't.

But if scientific consensus was the aim of the session, it missed by a light-year. And if advice is what Ruckelshaus was after, he had a variety from which to choose.

The panel of experts argued mightily over the accuracy of their atmospheric "models," the computerized maps by which they predict the path of traveling pollution. They disagreed over how much reduction in sulfur dioxide, believed to be the key precursor to acid rain, is necessary to protect sensitive areas.

Dr. Ruth Patrick, an aquatic specialist with the Academy of Natural Sciences in Philadelphia, even edged into semantics. "There's no such thing as a dead lake," she argued. "There's something living in every lake. The life form may be different, perhaps, or sparse, perhaps."

By the end of the session, Ruckelshaus was saying that scientific accord wasn't the point at all.

"What we're doing here is trying to assess the risk," he said. "There's clearly a risk. If there's one consensus here, it's that there is a problem."

At President Reagan's direction, Ruckelshaus has made acid rain one of his top priorities at the EPA. Shortly after taking office two months ago, he appointed a special EPA task force to review the administration's options for controlling acid rain, and he said yesterday he expects to have the group's recommendations ready for White House consideration "before the summer is out."

But he said the session underscored the need for additional study of the phenomenon, and added, "I have not come to a conclusion on research versus action."

Keyworth, however, suggested that the administration was ready to edge into action. Reagan, he said, is "anxious to deal with the problem of acid rain."

Last month, a scientific review panel appointed by Keyworth urged the White House to take immediate steps to reduce sulfur dioxide emissions before ecological damage becomes irreversible. Yesterday, Keyworth said that the panel's report, which called for an immediate reduction in sulfur dioxide under "least-cost" approaches, had been endorsed by Canadian scientists.

Meanwhile, a dozen bills are pending in Congress on the subject, some calling for more research and others outlining sulfur dioxide cutbacks of as much as 50 percent over a decade.

The scientists yesterday did find occasional points of agreement, among them the key conclusion of an Academy of Sciences report last month that there is a direct or "linear" relationship between the amount of sulfur dioxide that goes up and the acidity of the rain that comes down.

But there was occasionally sharp disagreement on whether current evidence clearly points to coal-fired boilers in the Ohio Valley as the prime culprits in acid rain damage to the north and east, and whether current computer models are good enough to gauge the effects of any regional or national sulfur-cutting effort.

Those are the critical points in the acid rain controversy as it moves out of the laboratory and into the halls of Congress, but some of the scientists yesterday suggested that science will not be of much further immediate help to government decision makers.

"We don't know the magnitude of the cuts needed or how long it'll take," said Dr. James Galloway of the University of Virginia. ". . . I'm not sure we'd solve all the problems by reducing sulfur."